Riddled TV Repair Forum

GBertolet · Joined: 25 Jun 2011 Posts: 25 Location: Pennsylvania

On my Zenith SC2793p set, the woofer circuit in the 9-569 Bose sound board went out. It keeps blowing the 3A inline fuse after several seconds when all speakers are connected, but holds when just the two tweeters are connected, and the woofer disconnected. Before the fuse blows, all 3 speakers are working fine. I want to replace two transistors in particular, Q3 and Q4 on the woofer circuit of the board. Q4 is split. Q3 has 8506 and NSDU51 on it, with a A and +503 on the back, and Q4 has 8504 and 112999 on it, with a D and +443 on the back. I believe they are supposed to be a matched set. Both have heat sinks. NTE gives 123AP for a sub for 8504, but I don't think it's correct. It doesn't even look right. 8506 shows no match at all, using NSDU51 shows NTE211. I don't know what is right. The Zenith schematic gives no description of the transistors on this particular board. With the information I have provided, can anyone ID these transistors and cross reference replacements? Thank you.

Google

JTS1957 · Joined: 21 Jan 2009 Posts: 2394 Location: Far, Far Away

8504 & 8506 are likely date codes. Fourth week of 1985.

http://www.searspartsdirect.com/partsdirect/part-number/NSDU51/0057/528?pathTaken=directMatch&filterPart=&pop=flush&prst=0&shdPart=NSDU51
Note that they say 112998 is a substitute. They also list the other transistor (112999) on the same site.

GBertolet · Joined: 25 Jun 2011 Posts: 25 Location: Pennsylvania

Thanks for the response JTS1957. The TV was made in 1986, so the date code is about right. I never believed Sears would carry any of these type of electronic parts. Surprising, at least to me anyway. I just ordered them. Hope to have them by the weekend. Thanks again.